Order field got multilpe same query

### Did you find a bug?

Yes

I use Mongodb for database. When I click sort random column. It got more then 10 queries all same. My table have more than 5 millions record so it took very long time to finish

### Expected behavior

Should be 1 query

### Actual behavior

[our bug report template]: https://github.com/activeadmin/activeadmin/blob/master/tasks/bug_report_template.rb